Antenatal steroid
Medications that mature fetal lungs before preterm birth.
Antenatal steroids, also known as antenatal corticosteroids, are medications given to pregnant women when preterm birth is expected. They accelerate fetal lung maturation, reducing the risk of infant respiratory distress syndrome and infant mortality. Their effectiveness was first demonstrated in a 1972 randomized controlled trial using betamethasone.
Quick Facts
- Synonym
- Antenatal corticosteroids
- Specialty
- OB/GYN
Facts from the source article.
Uses
Antenatal steroids reduce the occurrence and mortality of infant respiratory distress syndrome, a life-threatening condition from underdeveloped lungs. Current evidence indicates they lower the risk of late miscarriages and baby deaths, and decrease the likelihood of respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, and systemic infections in the first two days of life. They do not appear to increase maternal infection of the fetal membranes or womb. A single course given when preterm birth is expected before 34 weeks reduces child death risk regardless of resource level. Further research is needed for multiple pregnancies, but guidelines recommend use regardless of multiple gestation. In preterm premature rupture of membranes, steroids reduce neonatal mortality, intraventricular hemorrhage, and respiratory distress syndrome.
Adverse effects
Preliminary research suggests possible adverse long-term effects. In animals, antenatal corticosteroids have been linked to cardiometabolic issues, inhibited brain growth, and worsened memory and learning. Human preterm fetuses may face greater risk of mental and behavioral disorders during childhood, as the drugs enter the fetal brain and could affect neurodevelopment. Repeated doses may increase long-term risk of vision and hearing issues. Contraindications include systemic maternal infection and maternal chorioamnionitis.
Drugs
Corticosteroids encourage lung development in premature fetuses and are given when delivery is expected within 24 to 48 hours. Optimal benefit starts 24 hours after administration and lasts 7 days. In some regions, they are used up to 36 weeks of pregnancy. Common corticosteroids are dexamethasone and betamethasone. Dexamethasone is often recommended for its efficacy, safety, availability, and low cost, while betamethasone better prevents brain softening in premature fetuses. Both traverse the placenta and have very similar molecular structure, differing by one methyl group on betamethasone. Betamethasone has a longer half-life, but evidence is inconsistent on which is superior; a Cochrane review found unclear differences, while other studies suggest betamethasone yields better long-term outcomes. The drugs act on type II pneumocytes in alveoli, increasing cell maturation and production of mRNA for surfactant synthesis. Surfactant, a phospholipid-rich substance, increases lung elasticity and reduces surface tension, preventing alveolar collapse during exhalation. Preterm infants often lack sufficient surfactant, leading to respiratory distress syndrome; antenatal steroids boost surfactant production, improving outcomes.
History
In 1969, Graham Liggins began investigating dexamethasone effects on labor timing in pregnant sheep, testing his hypothesis that the fetus induces labor. Dexamethasone caused premature delivery, but the extremely premature lambs were born alive. With pediatrician Ross Howie, Liggins conducted a similar trial in 282 women projected to deliver preterm. This trial showed that betamethasone administration produced statistically significant improvements: lowered neonatal mortality, reduced respiratory distress syndrome (only in fetuses under 32 weeks treated at least 24 hours before delivery), and reduced intraventricular cerebral hemorrhage. These findings were reported in a 1972 article in Pediatrics. The research proved that antenatal corticosteroids decrease respiratory complications and infant mortality by inducing cellular differentiation and lung maturation, though the results were not incorporated into US clinical practice for over two decades.
More in Pathology of Pregnancy, Childbirth and the Puerperium
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